258 STRATIGRAPHICAL GEOLOGY 



erosion, and is overlain by a bed of rolled shells and limestone 

 pebbles with occasional quartz pebbles ; it was first found at 

 Castleton, but has since been traced by Dr. W. Hind through the 

 whole of Derbyshire and North Staffordshire. It contains many 

 Brachiopods, trilobites, and teeth of Psammodus, Psephodus, etc., and 

 shows that the current which brought the muddy sediment of the 

 overlying shales was at first strong enough to break up and destroy 

 some of the previously formed limestone, which at that time was, 

 of course, in an unconsolidated condition. 



The shales above mentioned are termed the Yoredale shales 

 by the Geological Survey and the Pendleside shales by Dr. W. 

 Hind, but as we shall presently see that the two groups are con- 

 temporaneous and not successive, as Dr. Hind supposed, it does 



w. 



Glacial Sands an 



Astbury 

 Fault. Limevrorks. Quarry. Quarry. 



: 1 : E. 



Trias 

 Fig. 88. SECTION THROUGH CONOLETON EDGE (by W. Gibson and W. Hind). 



n, i. Millstone grits. & to/. Grit, tuff, limestone, and shale. 



g. Pendleside shales. a. Main Avonian limestone. 



not matter which name they bear. The relation of these shales to 

 the limestone below and the Millstone grit above is shown in 

 Fig. 88. 



3. South Lancashire and Yorkshire 



The Avonian Series is brought up again from beneath the 

 Millstone grits in Lancashire and West Yorkshire (see map, Fig. 

 87) by an anticlinal flexure which runs in a north-easterly 

 direction from near Blackburn by Clitheroe to Skipton, with a 

 more northerly prolongation by Cracoe across Wharfedale by 

 Burnsall. From these places this division of the system spreads 

 northward and occupies a large irregular tract of ground varying 

 from 15 to 30 miles in width through Yorkshire, Durham, and 

 the eastern parts of Westmoreland and Cumberland. 



The rocks of this large area present two different facies, one in 

 the south-west, which has been called the Lancashire or Clitheroe 

 type, and the other to the north, which is known as the Yoredale 

 type. Moreover, the transition from one to the other is rapid, 

 and coincides closely with the line of the Craven fault, which 

 runs obliquely across the area from near Kirkby Lonsdale by 

 Ingleton, Stainforth, and Lin ton. South of this line the beds 



